Compressive performance of eccentrically double-cell concrete-filled circular steel tubular columns

Abstract

This paper presents a series of tests conducted on axial compression of concrete-filled steel tubes with double inner circular steel tubes (DIC-CFST) stub columns. The DIC-CFST stub columns are composed of four elements: an outer circular steel tube, two inner hollow circular steel tubes arranged symmetrically along the diameter of the outer tube, and concrete filling the space between the three steel tubes. A total of 27 specimens with varying eccentricity ratio (e), hollow ratio (ψ), and concrete strength (C) were subjected to the tests. The results indicate that under axial compression, noticeable local buckling failures occur in both the inner and outer steel tubes. Concrete failure manifests as vertical through cracks and circumferential crushing zones. The load-deformation curve of the specimens remains essentially the same as that of a full-section concrete-filled steel tube. A general positive correlation exists between the ultimate bearing capacity and the strength of concrete, and the range of eccentricity ratio and hollow ratio significantly influences the relationship between these two parameters and the ultimate bearing capacity of the specimens. As the concrete strength increases, the initial stiffness exhibits a noticeable increase. Conversely, the initial stiffness experiences a significant reduction with an increase in the hollow ratio. The ductility decreases with increasing concrete strength and eccentricity ratio. Furthermore, in comparison to the AISC 360–10 Specification, Eurocode 4, and Han's method, the calculation formula proposed in this paper for determining the ultimate bearing capacity of DIC-CFST stub columns has exhibited superior accuracy.